The field of the invention relates to a balanced antenna assembly for use in electronics applications generally, and for use in Bluetooth-compatible wireless modules, particularly.
A global de facto standard for wireless connectivity, Bluetooth is a short-range wireless communications specification adopted by Ericcson and later adopted by the Bluetooth Special Interest Group. Using a low-cost, short-range radio link, Bluetooth cuts the cords that used to tie up digital devices. When two Bluetooth equipped devices come within 10 meters range of each other, they can establish a connection together. And because Bluetooth utilizes a radio-based link, it doesn""t require a line-of-sight connection in order to communicate. A Bluetooth-compatible laptop, for example, may send information to a printer in the next room. Alternatively, a microwave could send a message to a mobile phone telling a user that a meal is ready.
An important difference between wireless and wired communications is that a wireless device has a transmitting and a receiving portion, as well as an antenna for performing wireless signal communications. Conventionally, the antenna is a dipole formed by a metal rod or a helical cylinder extending out from the wireless device. Extendable antennas, however, suffer from a number of disadvantages, including: increased overall size of the wireless device, and a tendency to break off or to pierce a user of the wireless device, among others. The next generation of conventional antennas were folded within the housing of the wireless device. Though these retractable antennas could be drawn from the housing by the user, users often find it impractical to do so. As a result, reception sometimes suffers.
The third generation of antenna technology is a xe2x80x9cprinted-circuit antenna,xe2x80x9d sometimes called a xe2x80x9cpatch antenna.xe2x80x9d Such antennas are desirable because they are lightweight and often have a high directivity. Examples of printed-circuit antennas include: U.S. Pat. No. 6,252,561 to Wu et al., which is an example of a rectangular loop antenna printed on a dielectric substrate; U.S. Pat. No. 5,495,620 to Couture, which is an example of a simple dipole antenna realized in the form of a printed circuit antenna; U.S. Pat. No. 5,206,657 to Downey, which shows a printed circuit radio frequency antenna comprising a pair of double sided printed circuit boards spaced apart by standoffs; and U.S. Pat. No. 4,758,843 to Agrawal, which shows a planar printed circuit substrate having a plurality of dipole antennas and a feed network including a sum and difference hybrid printed circuit thereon.
The disadvantage of these and other prior art antennas is that they do not meet the stringent design goals of the Bluetooth specification, which requires that the cost of Bluetooth transceivers (and their corresponding antennas) approximately match the cost of the wire tethers they are designed to replace. This requirement imposes stringent design goals for the Bluetooth 2.4GHz transceiver, its microcontroller, and memory requirements, as well as the external antenna system that accompanies it. In order to meet this design specification, the external antenna structure must be carefully designed as an integral subsystem to complement the overall Bluetooth system design, which is encapsulated in a packaged semiconductor Radio Frequency Integrated Circuit (RFIC).
For example, known antenna designs for Bluetooth devices include simple metal notch, F-style, or L-style radiating elements. However, these radiating elements are highly unbalanced and cannot be used in a Bluetooth module. In principle, a simple dipole having a terminal impedance of about 73 xcexa9 or about 300 xcexa9 if folded can be utilized. At the 2.402 to 2.480 GHz Bluetooth frequencies, however, such a dipole measures approximately 60 mm long. For most Bluetooth devices, such dipole dimensions are extremely long, and do not satisfy the Bluetooth specification. Moreover, a particular system architecture may require separate radio frequency (RF) ports for the receive and transmit half-duplex functions. Additionally, the inactive impedances, (e.g., the input impedances of the semiconductor devices in their unbiased states) may not be very large because of the residual package parasitics. Thus a solution is needed that provides a balanced antenna structure having significantly reduced physical dimensions.
An antenna assembly and methods of use are disclosed. In one embodiment, the antenna assembly is formed on a substrate and includes a first metal region and a second metal region attached to a surface of the substrate. The second metal region may be separated from the first metal region by a gap. The second metal region may include a first pronged end and a second end that correspond, respectively, to a first pronged end and a second end of the first metal region. The pronged ends of each metal region are connected to the differential inputs and outputs of a transceiver coupled with the antenna assembly.